Telephone call transmitter



Aug. 15, 1944. F. A. HUBBARD- 2,355,976

l TELEPHONE CALL TRANSMITTER Filed BeC. 25, 1942 Recs/VER 6 s; d

A TTOR/VEV Patented Aug. 15, 1944 UNITED STATES PATENT GFFICE TELEPHONE CALL TRANSMITTER Application December 26, 1942, Serial No. 470,247

8 Claims.

This invention relates to telephone call transmitters and is an improvement over the telephone call transmitter disclosed in an application filed in the name of R.. F. Mallina, March 22, 1940, Serial No. 325,347.

In the transmitter described in that application a set of key members is used for actuating U-shaped bars in predetermined combinations for releasing normally pretensioned vibrative elements in similar combinations, by the operation of latch members or pawls normally holding the vibrative elements in their pretensioned positions, the operation of the vibrative elements in the magnetic field of a generator being effective to transmit signals corresponding to the numerical Values of the successively operated key members.

In the transmitter of the Mallina application a U-shaped pivotally mounted bar is held by a retractile spring in operable relation to each of the ten digit key members so that when any one of the key members is depressed, such bar is operated to cause the operation of off-normal contacts which are instrumental in disconnecting the talking circuit of the subset from the line extending to the central oflice and in connecting the eld winding of the generator with the line. Thus during the time that any key member-is held depressed, the generator is held connected to the line and the talking circuits of the subset are rendered ineffective.

,In the circuit disclosed in Patent 2,232,398, granted on February 18, 1941, to A. A. Lundstrom, it has been proposed to provide the substation set with a copper-oxide rectifier bridge which in conjunction with the application to the line at the central office of current of a particular polarity serves in effect to disable the talking equipment of the subset when the generator is being employed under the control of the keyset key members to transmit digit signals over the line.

There are some conditions, particularly in stepby-step type dial systems, in which it is di'icult to provide that the same battery potential shall always be used on incoming calls, which would preclude the effective use of substation equipment of the type disclosed in the aforementioned patent. An off-normal contact arrangement such as is disclosed in the application of Mallina, above lreferred to, could be used in such step-by-step whereby the established connection might become released.

It is therefore the object of the present invention to provide a simple and efcient oir-normal switch mechanism whereby the talking equipment of the subset is disabled and the signaling generator is enabled upon the depression of any keyset key for a timed interval of only suiicient duration to enable the transmission of the digit signal by the generator.

A further object of the invention is to provide substation equipment so arranged that during the signaling interval there is no direct current bridge of the line at the subset through the transmitter and no circuit through the receiver and therefore no possibility of any interference between the talking and signaling circuits of the subset.

A further object of the invention is to provide substation equipment so arranged that the usual type of dial tone may be transmitted to the substation upon the initiation of a call and prior to the start of keying but which dial tone is readily removed as soon as a digit key is depressed to transmit the rst digit signal.

'I'hese objects are attained by the provision of a timed mercury Contact switch element of the transfer type disclosed, for example, in Patent 2,295,602, granted September 15, 1942, to C. E. Pollard, Jr., which switch element is arranged upon its operation to be fast to break its back contact and to make its front contact, but upon its release to be slow to break its front contact. For controlling the operation of the switch element, it is mounted in aligned holes in two parallelly disposed pole-pieces secured to the opposite polar ends of a permanent magnet. Normally the flux generated by the permanent magnet is shunted away from the magnetic circuit through the switch element by a soft iron armature normally held under the tension of a spring and also by magnetic attraction in engagement with the ends of the pole-pieces. To permit the operation of the switch element, the armature is mounted to be eammed out of engagement with the ends of the pole-pieces by a cam member pivotally mounted on the end of an arm secured to the U-shaped off-normal bar which is depressed whenever any one of the ten digit keys of the keyset is operated. The cam member is so pivoted with respect to a stop pin and to an associated leaf spring that the member only momentarily moves the armature away from the pole-pieces during the depression movement of any key but moves idly when the off-normal bar is restored by its associated retractile spring upon the release of the operated key without recamming the armature away from the pole-pieces. The tubular armature of the switch element is thus attracted only momentarily during the depression of a digit key to transfer the line loop from the talking equipment of the subset to the generator but since the switch element is of the type which is slow to open its front contact and slow to close its back contact following the release of its armature the generator is maintained connected to the line loop and the subsetl is disconnected from the loop only for the interval determined by its slow-to-release characteristic.

To further insure that there shall be no undesirable direct current bridge across the line loop through the generator at the substation, a condenser is interposed between that conductor of the line loop which is not disassociated from the generator by the olf-normal switch assembly and one terminal of the generator, thus during the time that the generator is being operated to )transmit a signal, the severing of all direct .current bridges at the subset may be utilized to discontinue the usual dial tone and as a signal that the voice frequency signals may be expected.

For a clearer understanding of the invention, reference may be had to the following detailed description taken in connection with the single sheet of drawings in which:

Fig. l is a side elevation of the telephone call transmitter embodying the invention, the casing being shown with a portion broken away;

Fig. 2 is a side elevation of the off-normal switch assembly with a portion thereof broken away to disclose the operating cam member;

Fig. 3 is a top plan View of the oli-normal switch assembly and a portion of the off-normal U-bar;

Fig. 4 is a side View partly in cross section of the mercury switch element constituting a part of the off-normal switchV assembly; and

Fig. 5 is a circuit diagram showing the application of the olf-normal switch thereto.

The transmitter to which the invention is applicable is provided with a base 25 having upturned edges to which the molded casing 2! is attached. Secured to the base is a mounting plate 22 having Iupturned ears 23 and 25, of which only ear 24 is disclosed, for supporting a shaft25 on which the key members Kl to KHE, inclusive, are pivotally mounted; an upturned and then inturned bracket 25 on the horizontal inturned end of which the off-normal switch assembly is secured as by screws 21; and an upturned plate 28. Ten key members K! to KHE? are provided but only two of such members K5 and Kl@ appear in the drawing. Each of the key members is normally and yieldably maintained in the position disclosed by a retractile spring 29, each of which springs is hooked at one of Vits ends to a key member and at the other of its ends to the upper edge of the plate 28.

' Also pivotally mounted on the shaft 25 are ve U-bars Bi to B5, inclusive, only the bar B5 appearing in the drawing, which are operable in dilerent combinations fupon the depression of the key `members to pluck the vibrative reeds of the'generator G, disclosed schematically in 5, in the manner fully described in the Mallina application hereinbefore referred to. Inasmuch as the present invention is not specically concerned with the reed plucking mechanism, such mechanism has not been disclosed.

Also pivotally mounted on the shaft 25 is a AU-shaped off-normal bar B5 which is held in operable relation with each of the ten key members, such as K5 and KIQ, by a retractile spring 55 which is hooked at one end to the arm 5l secured by rivets 32 to one arm of the bar B6 and hooked at its other end to the plate 28.

The olf-normal switch assembly secured to the bracket E5 has tWo parallelly disposed polepieces 33 and 34 clamped at one of their ends to the opposite pole-faces of a permanent bar magnet 35 by the screws 21. The pole-pieces 33 and 54 are L-shaped, as disclosed in Fig. 3, and have aligned holes in their inwardly extending arms in which the mercury contact switch element 35 is positioned. Cooperating With the end laces 31 and 38 of the pole-pieces is a soit iron armature 39. The armature is secured in any desired manner as by screws 40 to the outer end of a member 4i, the inner end of which is provided with parallelly disposed ears 42 by which such member is pivotally supported on the pivot screw (i5. bracket M secured to the mounting plate 22 by the screw 45, through aligned holes in the ears :i2 of the member l and into a threaded hole in the plate 22. For holding the armature 39 normally in engagement with the pole faces 31 and 38 of the pole-pieces 33 and 34, a retractile spring 51 is hooked at one end to the outer end of member lil and at its other end to the ear 58 extending upwardly from the outer edge of the pole-piece 34.

For camming the armature 39 away from the pole faces of the pole-pieces, the off-normal bar B5 is provided with a depending arm 59 secured thereto in any suitable manner as by screws 55, the lower end of which is provided with a portion 5i bent at rig-ht angles therefrom to lie in a Vertical plane. Pivotally secured to the portion 5| of arm d5 is a cam member 52, the camming portion ofw'hich, as disclosed in Fig. 2, extends through an opening in the member l! and engages with the upper edge of a camming portion 53 of the member 4 I. Normally the other end of cam member 52 is held against the stop pin 54 secured to the portion 5l of arm t9 .by a leaf spring 55 also secured to the portion 5l.

The mercury contact switch element 35 of the olf-normal switch assembly, as previously stated, may be of the type disclosed in the patent to Pollard hereinbefore referred to, having an envelope 56 of glass or other suitable material within which is a guide sleeve 51 entirely open at its upper end and partially closed at its lower end to add rigidity thereto and supported on and secured to the upper end of terminal wire 58. The wire 58 isr sealed-through the bottom of the envelope 55. The guide sleeve 51 is made of a material such as nickel which is wettable by mercury. Sealed through the upper end wall of the envelope are two parallelly disposed contact members 59 and 60 having their ends which extend into the envelope bent at right angles toward each other to form two stationary Contact portions 5I and 52, the upper one B2 of which serves as a front contact and the lowerone 6I of which serves as a back contact. The contact portion 62 is wide but the contact rportion 6I is narrow. Movable within the guide sleeve 51 is a cylindrical tubular armature 63 the ends of which are entirely open. The armature is made of magnetic material but its surfaces are such that they are readily wetted by mercury. Secured to the inner surface of the armature and movable therewith is a contact member 64 which may be formed ,by doubling a length of wire, bending the looped The screw 43 extends through a hole in the `end at right angles and'flattening the same provide a widened contact portion B5 'foi-engagei ment with the contact portions- 6l andE 62' ofthe back and front contact members 59 and Alll; A contact of this type has the property of conduct# ing mercury along the capillaryV ducts formed therein Yto its upper contact portion from which 'a small amount of mercury is transferred tothe surfaces of the contacts with whichit cooperates.

To ,complete the switch element a measured amount of mercury 66 is deposited; inl the bottom of the envelope. The'envelopeisthenevacuated, relled with a gas such as hydrogen to'a required operating pressure and thenA sealed.

With the measured amount of mercury'in theen velope, the mercury rises within the guide sleeve 51 and within the tubular armature-63to thepositions illustrated in Fig. 4' andV themercury is also conducted by the capillary action of the in-l ner surface of the guide sleeve 51 andthe outer surface of the armature 63 to lill the entire space between such surfaces. The surface tension of thefmercury between the upper edges ofthe-guide 'sleeve 5T and armature 63 and the surface ten.- 'sion of the mercury within the armature exerts a' downward' pull upon the armature to normally hold the contact portion 65 rmly againstA the 'contact 6I of the back contact member 59: The `mercury within the armature also engages the lower end of thecontact member E4 whereby mercury is carried along such member to-its upper contact portion 65 and in the normal position 'of the armature to the Contact portion 61 thereby establishing a mercury contact between the contaet'members 65 and 6l and thus betweentheterminaly wire 58 and the back contact member-5S. When the armature 39 of the olf-normal switch assemblyis cammed away from engagement with the pole-pieces, most of thefluX generated by *tl-'1e `permanent magnet 35 is permitted` to pass through the armature 63r of the switch element and the armature rises within thelguide sleeve 51 to center itself within the magnetic ''eld thus created, but will be restrained by the pull ofthe surface tension of the mercury pool and the surface tension of the film between the armature 63 and the sleeve 511, but this restraint is not sopgreat but that the film of mercury between the contact portion 6I ofv the back Contact member'59 and the contact portion B5 of the armaturecontact member 64 will disrupt quickly since `the cross-sectional area ofthe lm adjacent to the contact portion 6l is small. The armaturewill therefore move the contact portion 65 of the cenvtact member 64 quickly out of engagement with the contact portion 6l 4of the back contact mem.- yberr59 and into engagement with the Contact portion 62 of the front contact member 60". Mer cury adheringto the contact member 65 is now transferred to the front contact member 6'2 to establish a lm of mercury therewith..

Since the armature` 39 isv cammedaway from the pole-pieces 33 and 34 onlyy momentarily, it is quickly restored to establish a lowA reluctance shunt of the armature 63 of the switch element whereupon with the magnetic pulllon the armature 63 greatly reduced the surface tension ofth'e ymercury pool tends to pull the armature lyback into its normal or retracted position, but' since; the contact areas, of the Contact portions (i2-randJ 65 are both relatively large, the film of mercury be tween them will persist unbroken due to mercury drawn into the lm up the ducts of the member 'Ell-while the armature 63 moves in its retractive @movement under the influence of its weight and with the first digit the surface tension of the mercury pool until the film nally breaks whereupon the contact portion 65 snaps quickly into engagement with the contact portion 6.I of the back contact member 59. This switch element thereforev effects a quick make and aslow break of its front Contact closure lwhich break should be in the order of 30 or 40 milliseconds and a quick break and slow make of itsback contact closure.

The application of the improved call transmitter to a telephone systern-hasbeen schematifcally illustrated in Fig. 5: in which the box marked Subset illustrates the usual talking equipment Vof the substation instrument and the apparatus within the-dot-d'ash rectangle illustrates the keyset equipment of the substation instrument includingf the signal generator G having ve selectable reeds pluckablein different combinations by the key members of the keyset and the contacts El; 62 and B5 of the oi-normal switch assembly. One terminal of theV generator G is connected to the tip conductor T of the substation line through the condenser C and the other ter- `minal is disconnected from the ring conductor R of the line at the normally open contacts 62 and 65. The subset is normally bridged across the tip and ring conducto-rs of the line through the normally closed contactsy 6I and 65.

, When the subscriber lifts the handset from the cradle of the substation instrument, a circuit is 'established through the subset and over the line which in the usual manner is instrumental in causing a line` nderat the central office to find the calling line and to cause the extension of a connection from such line to an idle central oflice sender which may be employed to control the establishment of a connection from the calling line in `accordance with the digits of a called line number keyed by the Vcalling subscriber. Upon the establishment of a connection from the calling line to the sender, a circuit is established from battery through the left winding of relay 61 over the ring conductor R of the line through the subset, contacts 6|V and 65 of the off-normal switch assembly, tip conductor T of the line, through the right winding of relay El and over the normal contacts of relay 68 to ground lthrough the primary winding of the dial tone coil '69. Relay 6l thereupon operates and establishes `an obvious circuit for slow-to-release relay l0 Ywhich operates to close the usual holding circuit for the sender. The calling subscriber also receives dial tone transmitted from the dial tone coil G9 over the previously traced circuit to inform him that he may proceed tokey up the vwanted subscribers number.

Upon the depression of a k-ey'in accordance of the wanted line number, the off-normal bar BB is operated thereby moving cam member 52 carried thereby downwardly and, since the cam member engages with the upper edge of the cam portion 53 of the armature such cam member tends to rotate in .a counter-clockwise direction.

Since, however, the cam member 52 is prevented from rotating in `a counter-clockwise direction by the stop pin 54, the cam member is effective in its downward movement to cam over the camperstion 53 and thereby move the member 4l to move the armature 39 carried thereby@ away from its bridging engagement with the pole-pieces 33 and 34. The armature 63 o-f the switch element 36 is thereupon quickly moved to a position in which the cen-tact portion S5: is disengagedV fro-inthe contact Si of the back Contact member 59land1is engaged with thecontact portion 62 of the front contact'member 60. The loop circuit through the subset is now opened vand the keyset generator G is'bridged 'across the substation line through the condenser-C.

With the direct current bridge of the line now interrupted, relay 61 releases but relay 19 being slow to release remains operated for an interval determined by its slow-to-release'characteristic whereby the circuit of the dial tone removal relay 68 is established from ground over the inner left back contact of relay 61, over the right contact of relay through the winding of relay 68 to'battery. Relay 68 upon operating locks over its outer contacts to groundvover the inner left contacts. of relay 10, disconnects the primary winding of the dial tone coil 69 from the previously traced circuit through the right windingof relay 69 and substitutes a direct ground connection therefor. A circuit is also established at thisv time over the outer back contact of relay 61 and the outer left front contact of relay 10 to prepare the receiving circuit 1| for receiving signals transmitted by the generator G in response to the keying of digits of the wanted line number.

-As the cam member 52 continues its downward movement in response tothe depression ofthe keyset key, it moves past the cam portion 53 of the member 4l thereby permitting the spring 41 -to restore the member 4| to reeng'age the armature 39 with the pole-pieces 33 and 34. The armature 63 of the switch element 36 being now 'magnetically shunted by the armature 39 tends to retract to its normal position and to move the contact portion 65 out of engagement with the contact portion 62 of the front contact mem- -ber 60 but this retraction is delayed suiciently by the retarded breaking of the mercury film between such contact portions as to insure that sufficient time is lallowed to permit the generator G to transmit the alternating current Vsignal .under the control of the depressed key of the `keyset. As soon as the mercury film becomes sufficiently attenuated it erupts and the contact .portion moves into engagement with the contact portion 6I thereby disconnecting the generator G from the line and reconnecting the sub- ',set therewith. Relay 61 is thereupon reoperated to reestablish the circuit of relay 10. The interval during which relay 61 is thus deenergized is not sufficient to permit the release of relay 10 so that the holding circuit of the sender is maintained closed.

When the depressed key is released, the 01T- fnormal bar B6 is restored to normal by the spring 30 thereby raising the cam member 52, -the end of which now engages the lower edge of the cam portion 53 of the member 4l and the -cam member-52 is thus caused to rotate in a tated when rectiers were used; permits the use .of the ordinary dial tone and its removal when 75 signals are being transmitted by the generator; simplies the equipment for receiving the voice frequency signals, which equipment has heretofore required separate detecting circuits to recognize the presence of key signals, by providing an independent indication through the release of relay 61 of the sender while relay 10 remains operated that signals are to be expected and minimizes the possibility of false operation or distortion of signals.

, f What is claimed is:

1.v In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator, and a transfer switch operable in response to the depression of any key to first disconnect Vsaid subset from said line, to thereafter connect said generator to said line for a predetermined interval regardless of the length of timev the key is held depressed and to then reconnect said subset to said line.

2. In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator, a condenser and a transfer switch assembly operable in response to the depression of any key to first disconnect said subset from said line, to thereafter connect said generator through said condenser to said line for a predetermined interval regardless of the length of time the key is held depressed and to .then reconnect said subset to said line.

`3. In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator and a transfer switch assembly-including a mercury contact switch operable upon the depression of any key to first disconnect said subset from said line, to thereafter connect said generator to said line for a predetermined interval regardless of the length of time the key is held depressed and to then reconnect said subset to said line.

4. In a, telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator and a switch assembly for transferring said line from said subset to said generator, said assembly comprising a magnetic circuit including a permanent magnet, a magnetically con- `:trolled switch included in said magnetic circuit, 'a shunt of magnetic material normally positioned to shunt ux generated by said magnet away from said switch, and means controlled by the depression of any key for moving said shunt to permit the operation of said switch.

-5. In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator and a transfer switch assembly including a mercury contact switch element operable to first disconnect said subset from said line, to thereafter connect said generator to said line for a predetermined interval and to then reconnect said subsetto said line, and means for controlling a single timed cycling of said switch element in response to the depression of any key and irrespective of the length of time said key is held depressed.

6. In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a, key-controlled multifrequency current generator and a switch assembly for transferring said line from said subset to said generator, said assembly comprising a magnetic circuit including a permanent magnet, a magnetically controlled mercury switch element included in said magnetic circuit, and a shunt'of magnetic material normally positioned to shunt flux generated by said magnet away :from said switch element, and a cam member operable only in response to the depression movement of any operated key vto momentarily move said shunt away from said magnetic circuit to permit the operation of said switch element.

'7. In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator and a switch assembly for transferring said line from said subset to said generator, said assembly comprising a magnetic circuit including a permanent magnet, a magnetically controlled mercury switch element included in said magnetic circuit and a shunt of magnetic material normally positioned to shunt flux generated by said magnetaway from said switch element, an off-normal bar in said keyset operable upon the depression of any key, and a cam member associated with said bar operable upon the operation of said bar to momentarily cam said shunt away from said magnetic circuit to permit the operation of said switch element, but inoperative to cam said shunt away during the restoring movement of said bar.

8. In a telephone system, a subscribers line and a substation on said line comprising a telephone subset, a key-controlled multifrequency current generator and a transfer switch assembly comprising a magnetic circuit including a permanent magnet, two parallelly disposed polepieces connected to the pole faces of said magnet and having aligned holes therethrough, a mercury switch element supported in said holes having an armature, a contact member carried thereby and fixed front and back contact members, said armature upon its attractive movement moving its contact member quickly out of engagement 4with said back contact member into engagement with said front contact member and upon its retractive movement moving its contact member out of engagement with said front contact member after a predetermined interval, and a shunt of magnetic material normally positioned to shunt ilux generated by said magnet away from the armature of said switch element, and means controlled by the depression of any key for momentarily moving said shunt whereby said armature is momentarily attracted and released to transfer said line from said subset to said generator for a predetermined interval and to then transfer said line back to said subset.

FRANCIS A. HUBBARD. 

